The existing bibliography shows that the norelgestromin is a product of the metabolism of the norgestimate, which results of the hydrolysis of the acetyl group in the 17th position. [S. Madden and D. J. Back -J. Steroid Biochem. Molec. Biol. 38 (4), 497 (1991); M. J. Wild et al. -ibid. 39 (4 A), 535 (1991); M. J. Wild et al. -ibid. 45 (5), 407 (1993)].